A device has been proposed which displays the image of the surroundings of the host vehicle or the trajectory of the host vehicle to assist the driving of the driver when the driver parks the vehicle in the parking area. For example, Patent Literature 1 discloses a device which displays an estimated guidance trajectory when the vehicle is reversed with the steering angle fixed to a maximum value. The device disclosed in Patent Literature 1 displays peripheral information acquired by a sensor and the position of the host vehicle on a display screen. The device disclosed in Patent Literature 1 displays a guidance trajectory integrally with the symbol of the host vehicle on the screen such that the point where the guidance trajectory is accommodated in a parking space is a reverse starting position. In addition, the device disclosed in Patent Literature 1 also displays an estimated trajectory whose shape is changed depending on the actual steering angle of the steering wheel such that the estimated trajectory overlaps the guidance trajectory, thereby guiding a steering operation.